(a) Field of the Invention
The present invention relates to a photoconductive layer for a color display panel, more specifically, to a composition of a photoconductive layer for a color display panel which comprises a styrene-acrylic copolymer as an organic binder, a thioxanthene derivative as an electron receptor and a tetraphenylbutadiene derivative as an electron donor. This composition has a low decomposition temperature, high electron transferring ability and charge maintenance ability to produce a color display panel without change of brightness and color coordinates in a fluorescent screen.
(b) Description of the Related Arts
A fluorescent layer for a color display panel is manufactured using a spinning method of a slurry coating method. First, a panel of a glass bulb is spun, a photoresist such as polyvinyl alcohol and ammonium chromate is coated thereon, and the panel is heated and dried. The panel is assembled with a mask assembly to produce a panel-mask assembly and the photoresist thereon is exposed to ultraviolet (uv) rays through a mask slot in the form of a dot or a stripe to stick onto the panel. The assembly is washed with deionized water to remove the photoresist which was not exposed to uv rays, and dried. A space between dots (or stripes) is coated with a nonfluorescent photoabsorbent such as a graphite solution, dried by heating and washed with hydrogen peroxide. The panel is washed by a high pressure spray of distilled water to remove the photoresist and the graphite. The panel is dried by rapidly spinning to form a black matrix. Red, green and blue fluorescent materials are applied between the black matrices to produce a fluorescent layer. There are two methods to apply fluorescent materials to the black matrix, namely a slurry method and an electrophotographic method. The slurry method is carried out as follows. A red fluorescent material slurry is coated on a panel by rapidly spinning the panel at a constant speed. The panel is heated to dry the fluorescent materials and exposed to light using a mask. After exposing, the mask is removed and the fluorescent material which was not exposed light is removed using deionized water to produce red fluorescent material dots or stripes. The same process mentioned above is used to produce green and blue fluorescent material dots or stripes. The final panel is composed of thousands of dots or stripes. The exposure to light is identical with the above process except that the fluorescent material is exposed to light using a light source with a special angle and on the fixed point not to overlap three fluorescent materials. Finally, the fluorescent layer is dried to form a fluorescent screen. The diameter difference of central dot and peripheral dot on the fluorescent layer produced by this method is severe and the form of the dots is distorted to make lower color purity.
The electrophotographic screening process in which the drawback of the above slurry method is eliminated, is described as follows.
A conductive material is coated on an interior surface of a faceplate panel of a color display panel to form a conductive layer and a photoconductive material is overcoated on the conductive layer to form a photoconductive layer. Then, a substantially uniform voltage is applied to the photoconductive layer of the panel and selected areas of the photoconductive layer are exposed to visible light to affect the charge thereon, without affecting the charge on the unexposed area of the photoconductive layer. The fluorescent layer is formed by spraying a fluorescent material powder onto the exposed area of the photoconductive layer.
While the photoconductive layer makes roles of an insulator in the dark, an electrolyte emits electrons or holes in the light source of uv or visible rays.
The structure of a fluorescent layer for a color display panel comprising a photoconductive layer is described in FIGS. 3 and 4. The photoconductive layer comprises an organic conductive layer (13) and a charge originator/charge carrier layer (15) coated on a polymer dispersed charge originator and charge carrier in a color display panel (11) in FIG. 3. Hole or electron carriers such as hydrazone, styryl, pyrazorine, triphenylamine compounds may be added to the polymer. In addition, the photoconductive layer is formed to coat an electron donor (25) on the organic conductive layer (13) and to laminate an electron receptor (27) thereon. The electron donor (25) and electron receptor (27) are dispersed in a binder polymer. The hole or electron carriers such as hydrazone, styryl, pyrazorine, triphenylamine compounds may be added to the polymer as a supporter of charge transport.
A composition of photoconductive layer contains an organic binder, an electron receptor, an electron donor and a residual solvent. The general organic binders used are polyvinyl cabazole, polymethylmethacylate or polypropylene carbonate. The electron receptors used are hydrazone, styryl, pyrazorine, and triphenylamine compounds which have low molecular and conductivity, and are used for copy machines. The corona charge (-) process has to be carried out because these compounds transport holes, which produce a large amount of ozone. As a method to solve this problem, Japanese laid open Pyung 2-21486 and Sho 61-233750 describe trinitrofluorenone (TNF) and antraquinone derivative as electron receptors and dimethylphenyl diphenylbutatriene (DMPBT) as electron donors. The above electron receptors and donors are not enough to transport and maintain electron charges and to use with the polymer binder. The imperfect combustion of the photoconductive material coated on a panel occurs in the process for sealing of a panel/funnel at the temperature of 450.degree. C., because the dimethylphenyl diphenylbutatriene decomposes at high temperatures. Accordingly, more than 10% of the photoconductive materials remain thereby decreasing fluorescent brightness and color coordinate for a color display panel.